问题

最近在用kotlin写jni,但是生成头文件的时候遇到了些问题。
首先 javah 在java >= 1.9 就被取消用javac -h代替,但是javac对kotlin不适用,kotlinc也没有 -h 这个生成头文件的选项。

解决方法

在stackoverflow论坛找到了个解决方案,那个人提供了一个gradle task,大概原理是先用complieKotlin任务(或kotlinc)生成class字节码,再用javac编译回java文件,然后再调用javac -h 针对那个java文件生成jni头文件,我稍微修复了下,然后迁移到gradle kotlin dsl(就kts脚本),代码在下面。

使用方法

复制到build.gradle.kts的最外层就可以了,然后sync一下gradle,然后在gradle task里的build分类下就有generate jniheader这个任务了,StackOverflow原贴地址https://stackoverflow.com/a/65661275/14646226

需要改下代码里的inputs.dir("src/main/kotlin")到你的kt源码文件夹, outputs.dir("src/main/generated/jni")到你想的输出文件夹

代码

val generateJniHeaders: Task by tasks.creating {
group = "build"
dependsOn(tasks.getByName("compileKotlin"))

// For caching
inputs.dir("src/main/kotlin")
outputs.dir("src/main/generated/jni")

doLast {
val javaHome = org.gradle.internal.jvm.Jvm.current().javaHome
val javap = javaHome.resolve("bin").walk().firstOrNull { it.name.startsWith("javap") }?.absolutePath ?: error("javap not found")
val javac = javaHome.resolve("bin").walk().firstOrNull { it.name.startsWith("javac") }?.absolutePath ?: error("javac not found")
val buildDir = file("build/classes/kotlin/main")
val tmpDir = file("build/tmp/jvmJni").apply { mkdirs() }

val bodyExtractingRegex = """^.+\Rpublic \w* ?class ([^\s]+).*\{\R((?s:.+))\}\R$""".toRegex()
val nativeMethodExtractingRegex = """.*\bnative\b.*""".toRegex()

buildDir.walkTopDown()
.filter { "META" !in it.absolutePath }
.forEach { file ->
if (!file.isFile) return@forEach

val output = com.gradle.publish.plugin.dep.org.apache.commons.io.output.ByteArrayOutputStream().use {
project.exec {
commandLine(javap, "-private", "-cp", buildDir.absolutePath, file.absolutePath)
standardOutput = it
}.assertNormalExitValue()
it.toString()
}

val (qualifiedName, methodInfo) = bodyExtractingRegex.find(output)?.destructured ?: return@forEach

val lastDot = qualifiedName.lastIndexOf('.')
val packageName = qualifiedName.substring(0, lastDot)
val className = qualifiedName.substring(lastDot+1, qualifiedName.length)

val nativeMethods =
nativeMethodExtractingRegex.findAll(methodInfo).mapNotNull { it.groups }.flatMap { it.asSequence().mapNotNull { group -> group?.value } }.toList()
if (nativeMethods.isEmpty()) return@forEach

val source = buildString {
appendLine("package $packageName;")
appendLine("public class $className {")
for (method in nativeMethods) {
if ("()" in method) appendLine(method)
else {
val updatedMethod = StringBuilder(method).apply {
var count = 0
var i = 0
while (i < length) {
if (this[i] == ',' || this[i] == ')') insert(i, " arg${count++}".also { i += it.length + 1 })
else i++
}
}
appendLine(updatedMethod)
}
}
appendLine("}")
}
val outputFile = tmpDir.resolve(packageName.replace(".", "/")).apply { mkdirs() }.resolve("$className.java").apply { delete() }.apply { createNewFile() }
outputFile.writeText(source)

project.exec {
commandLine(javac, "-h", "src/main/generated/jni", outputFile.absolutePath)
}.assertNormalExitValue()
}
}
}

gradle task位置截图

gradle task